Experimental Study on the Process Parameters of Pneumatic Percussive Rotary Drilling in Coal Mine
The impact rotary drilling method is one of the main technical methods to solve the problem of low drilling efficiency of hard rock formations.In order to optimize the pneumatic percussive rotary drilling process parameters used for the drilling of hard rock through strata boreholes of coal mine underground,the test rock strata was divided into lower argillaceous sandstone,middle quartz sandstone and upper argillaceous sandstone by collecting the core of the test formation,preparing samples and conducting uniaxial com-pressive strength tests.The working principle of pneumatic percussive rotary drilling method and the characteristics of drilling tool com-bination were discussed.The main process parameters affecting drilling efficiency were analyzed,including gas pressure,drilling rig speed and feed pressure,and the level selections of each parameter in orthogonal test design were given.Using the technical idea of"longitudinal rate of penetration comparison and horizontal process parameter optimization",the process parameter optimization study was carried out by using the orthogonal experimental design method,and the rate of penetration and difference of each rock formation were analyzed.The results show that the influence of gas pressure on rate of penetration is significant,and the drilling rig speed and feed pressure are not significant,but the sensitivity of the drilling rig speed to the rate of penetration is obvious than the feed pressure.Through the study of process parameters,under the conditions of test equipment and drilling tools,the optimal process parameters are obtained:gas pressure is 1 MPa,drilling rig speed is 40 r/min,and feed pressure is 3.0 MPa.Through the study of the rate of pene-tration of each strata,it is obtained that the rate of penetration of the lower argillaceous sandstone is highest,the upper argillaceous sandstone is followed and the rate of penetration of the middle quartz sandstone is the lowest.The analysis believes that for the two kinds of sandstone with large argillaceous content,the higher the argillaceous content,the softer the rock,and the corresponding plas-ticity increases.For the method of percussive-based crushing,the greater the plasticity,the more unfavorable for the rate of penetra-tion,and the drilling efficiency is relatively lower.The upper argillaceous sandstone is in the deepest section of the test boreholes,and the drill bit wears more,which has an adverse impact on the drilling efficiency at the deep hole.
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